In, for example, a vehicle mounted car navigation system, a hands-free phone, or a telephone conference system, noise suppression is conventionally performed to suppress noise contained in a speech signal that has mixed-in noise other than a target voice (for example voices of people talking). Technology employing a microphone array including plural microphones is known as such noise suppression technology.
In such conventional noise suppression technology using a microphone array, there is a method for noise suppression based on an amplitude ratio between signals received from plural microphones. The amplitude ratio becomes 1.0 when the distance between each of the microphones and the sound source is the same distance or when far away, and the amplitude ratio is a value that deviates from 1.0 when the distance between each of the microphones and the sound source is a different distance. Noise suppression based on the amplitude ratio is a method that employs the amplitude ratio, and so, for example, when a target sound source is present at a position that has different distances to each of the microphones, the method suppresses noise that has a value of amplitude ratio of close to 1.0 in the received signals from the plural microphones.
However, even when the distances between each of the microphones and the sound sources are the same distances, sometimes the value of the amplitude ratio deviates from 1.0 due to sensitivity differences that arise between each of the microphones. Since accurate noise suppression based on amplitude ratio is not be performed in such cases, there is accordingly a need for technology to correct for such sensitivity differences between the microphones.
As technology to correct sensitivity differences between microphones, there is, for example, a proposal for a device that corrects the level from at least one sound signal by deriving a correction coefficient when performing audio processing based on sound signals respectively generated from sound input to plural sound input sections. In such a device, for respective sounds input to the plural sound input sections, frequency components are detected of sound arriving from a substantially orthogonal direction with respect to a straight line defining the placement position of a first sound input section and a second sound input section among the plural sound input sections. The direction from which the sound arrives is detected based on phase differences between the sounds arriving from the first sound input section and the second sound input section. In order to match the levels of sound signal respectively generated by the first sound input section and the second sound input section based on the sound of the detected frequency components, correction coefficients are derived for correcting the level of at least one of the respective sound signals generated from the input sound by the first sound input section and the second sound input section.